The present invention relates to irrigation systems, and more particularly, to an improved diaphragm flow control valve which can more conveniently and completely vent trapped air from the region above the diaphragm and below the bonnet.
The use of valve controlled pressurized irrigation systems for supplying water for the irrigation of plants is extensive throughout the world today. One of the most prevalent systems, particularly for lawn areas and athletic fields, includes a plurality of sprinklers positioned for distributing water over the surface of a land area. One or more control valves connect and disconnect water from a pressurized main supply line to branch lines each typically having several sprinklers connected thereto.
Pressure responsive and pressure regulating valves used in irrigation systems typically have a main diaphragm valve that is normally pilot operated. Upstream or inlet water pressure passes via a small metering orifice to the back side of a moveable diaphragm to apply valve closing pressure. The water is vented from the back side of the diaphragm via a small pilot valve passage controlled by a solenoid operated pilot valve to the main outlet passage of the valve. Hydraulically actuated diaphragm valves also vent water pressure from the downstream side of the diaphragm, without the need for a solenoid.
In diaphragm flow control valves it is not uncommon for excess air to become trapped between the upper side of the diaphragm and the bonnet, i.e. the upper generally hemispherical part of the main valve housing. The bonnet is also sometimes referred to as the upper clam shell. The inlet to the pilot valve passage is located too low to vent the trapped air. This trapped air can cause erratic behavior of the valve during its opening and closing cycles. If too much air accumulates between the uppers side of the diaphragm and the bonnet the valve can close too quickly, causing a water hammer effect that can damage downstream fittings and cause leaks.
In an effort to overcome this problem, diaphragm valves have been commercially produced with needle valves mounted in the bonnet. These valves can be manually opened to bleed air from between the diaphragm and the bonnet. However, since the needle valve is not located at the highest part of the bonnet but instead roughly halfway between the peak and its peripheral side edge, not all the trapped air can be released in this fashion. In addition, needle valves are relatively expensive and can rust, break and/or clog.
Accordingly, there is a need for a diaphragm flow control valve which can more conveniently and completely vent trapped air from the region above the diaphragm and below the bonnet.